Sheet metal formed parts, such as fender or hood panels in automotive applications, or a variety of other parts, are typically manufactured by way of drawing, stamping, deep-drawing, stretch-forming, or the like. The parts are typically manufactured from a flat sheet metal blank in several operations (including cutting, drawing, reshaping, trimming, flanging, etc.), within a forming press. To facilitate various aspects of the process, additional material is included together with the component design in order to control the material flow into the die cavity. This is done so that the component can be produced defect-free (no splitting, wrinkling, excessive thinning, etc.).
This additional material is termed the “addendum”, and is the material outside of the final part, and which connects the part, or component geometry, with a binder. The addendum geometry is of significant importance to a defect-free drawing process, since it is the main forming control mechanism to achieve quality products. The addendum provides continuity between the binder and the component.
For components with large cut-outs, such as body sides of passenger cars, internal addenda can also be created, in order to satisfy similar continuity requirements to the component, and an internal binder.
Optimization of the addendum design can result in improved control of the component thickness, strength, strain, stress, shape, and the like, and thus, the quality of the component can be controlled using these quality criteria. As such, with regard to design optimization, it is the addendum design which requires specific attention during the tooling geometry design.
The sheet metal tooling for the drawing operation typically consists of three parts: a die (female part of tooling), an optional binder or blank holder (to position and hold the sheet metal blank and/or to control material flow into the die cavity), and a punch (male part of the tooling that drives a typically metal (e.g. steel or aluminum) blank into the die cavity during the forming process).
The drawing process typically involves preparing a suitably shaped die punch which is pressed into a surface of the blank in order to create a component having the desired shape and appearance. The addendum is designed to ensure the desired shape and quality of the component part, is achieved from the blank.
It should be noted that the desired component shape formed from the blank has been pre-established. As a result, the component design does not typically change during the design of the addendum, and as such, the shape and design of the component per se, is generally outside of the scope of the present invention.
The blank can be flat, but more typically, is curved to generally follow the lines of the desired part. Moreover, it can also be shaped so as to facilitate the forming operation. Consequently, the blank is commonly pre-formed (usually curved) and fixed within the die. In fact, the blank may be pre-formed in an earlier operation of the sheet metal operation.
The blank is typically held at the edge of the blank in the binder, so as to avoid unwanted movement of the blank during the forming operation. As such, a binder is typically formed on the blank, and the blank usually conforms to the binder shape. In most operations, the surface(s) of the binder are normally continuous surfaces.
In the prior art, the component and binder shapes have been pre-established, and once established, the complex task of addendum design was initiated. This typically required the use of a sectional design approach, in which numerous vertical, planar section lines were used to connect the part edge, and the binder, so as to create a sectional profile for that part of the addendum. Once one section was designed, the operator would design an adjacent section, and the procedure would be repeated around the part. Afterwards, the vertical sectional lines would be inter-related, one to the other, so as to prepare a suitable addendum design geometry.
However, while this process would eventually provide a suitable addendum shape, the process was labour intensive. Furthermore, if the component design was modified, or its position, or orientation, or some other parameter was modified, the procedure of section line design would need to be re-initiated, so as to prepare a new addendum design.
Even with the advent of computerized systems, the design of the addendum geometry still required excessive time and labour. These initial systems again followed the traditional approach to design the addendum by using section lines originating from a point on the component edge and extending outward, and ending at a point on the binder. The section lines however, were usually normal to the component edge and projected in the direction of the drawing process. When these lines were inter-related, it was not uncommon to obtain twisted and/or badly interpolated addendum.
More recently, the computerized sectional approach has been improved as described in, for example, U.S. Pat. Nos. 7,623,939, 7,894,929 and 8,155,777, and in US patent publication No. 2012/0197602. The approaches described in these patents improved the computerized design approach by using non-planar section lines, and by allowing for transverse interpolation of the non-planar section lines. This approach was further improved by smoothing the component edge, by filling the surface areas at edge discontinuities, or modified via a rolling cylinder technique. This resulted in a well behaved and smooth outside component edge before the section lines are attached, and therefore substantially overcame the problem of having irregular and highly twisted addendum.
These approaches therefore provided at least some form of addendum design automation, and hence made it possible to use an optimization design procedure. These approaches also provided a solution to overcome the overlap of section lines around the concave component boundaries, by the use of non-planar section lines.
While these approaches have reduced the time and effort required for addendum design, all of these approaches are still based on a sectional approach in which section lines originating from the component edge and extending outward to the binder, are used. As such, even with the use of a computerized technique, addendum design is still somewhat cumbersome. Consequently, design and modification of the overall die design is still a skill and labour intensive process.
As such, while the art of addendum design has improved significantly over the last few years, proper addendum design continues to be a challenge, since addendum design, even when performed virtually using computer aided design (CAD) systems, still requires considerable effort.
For example, as a rule of thumb the number of addendum surfaces in CAD, is usually of the same order as the surfaces making up the component geometry. As such, for large body parts, the number of addendum surfaces can be considerable, and the design of the addendum still requires the involvement of a forming and CAD design specialist.
Other issues with the prior art approaches are known, as such, included in the problems associated with current computerized addendum design approaches, are the following issues:
i) the section lines require detailed definitions, and hence considerable efforts are expended in areas where such accuracy is not warranted;
ii) with the section line definitions, the draw depth, the connection to binder, the Punch and Die Opening Lines, among other thing, are extracted, as opposed to being inputted into the design definition. Accordingly any modifications to these parameters would necessitate re-definition of many sections. This limits the type of optimization that can be performed;
iii) the section based procedure adapts reasonably well to the case where the component geometry is on the punch face, but typically does not address the general cases where the component geometry covers other areas of the tooling, e.g. punch sides and binder;
iv) the procedure is still complex and requires considerable expertise, and hence does not lend itself to quick applications for sketching and cost engineering;
v) the technology typically requires too many inputs, and requires simplification in order for the system to be used by the non-specialist;
vi) the location, direction and number of section lines required around the component boundaries are not necessarily obvious to the non-specialists. For example, it is unclear to the unskilled user whether the section line directions are to be perpendicular to component edge, along principal geometry direction or along metal flow directions. It is also not clear to the non-specialist how the resulting addendum solution is dependent on, or affected by, such assumptions;
vii) the section line technology does not lend itself to the minimization and optimization of the punch face, before the finalized generation of the addendum, and hence to facilitating blank size reduction. Furthermore, the punch face is not readily defined but needs to be extracted from all the sectional profiles; and
viii) flange and hem features typically have to be removed prior to addendum design.
To overcome these difficulties, it would be advantageous to provide a method for addendum design, wherein the addendum can be designed and optimized in a more rapid, and less complex fashion. Further, it would also be advantageous to provide a method wherein design and optimization of the addendum was achieved with minor use of, or preferably, without the use of the section line approach. Still further, it would be advantageous to produce a method wherein the design of the addendum is more easily modified. Even further, it would be advantageous to provide a method for the design and modification of the addendum geometry which could be more easily related and modified based on simulated and/or calculated design parameters, and/or more easily modified based on parameter modification.
These and other advantages are provided by the methods and apparatuses of the present invention, as hereinafter described.